Two of the most basic goals of nuclear physics are to understand the mechanisms responsible for the formation of hadrons and explain their structure in terms of the gluons and quarks of quantum chromodynamics (QCD). In this connection, measurements of the nucleon excitation (N*) spectrum and exploration of N* structure through the study of resonance electroexcitation amplitudes (γvNN* electrocoupling parameters) on a broad domain of photon virtualities present unique opportunities for elucidating these crucial aspects of nonperturbative strong-interaction dynamics.

Pushing the idea of an electron microscope to higher and higher
energies allows us to investigate nucleons and their
excitations with higher and higher resolution via electron
scattering experiments carried out at the Thomas Jefferson
National Accelerator Facility (TJNAF) in Virginia. The contact
persons of this nucleon excitation program,
Ralf Gothe (USC) and Viktor Mokeev (JLab), have forged a close
collaboration of theorists and experimentalists that has already
started to reveal some of the remaining secrets of the strong
interaction that binds quarks into nucleons and nucleons into
nuclei. Among these secrets
are: what is the origin of more than 98% of the mass that
surrounds us, up to which distance scale are mesons contributing
to the formation of baryons, and how does nature confine colored
quarks.

Carrying out the next generation of experiments at Jefferson Lab that
might allow us to finally understand the strong interaction,
Ralf Gothe and his group are building a large-scale
time-of-flight detector here at USC with unprecedented time
resolution that will ensure proper particle identification in
all CLAS (CEBAF Large Acceptance Spectrometer) experiments after
the TJNAF upgrade to 12 GeV.

Selected Lectrures, Talks, and
Proceedings

Impact of the γvNN* Electrocoupling
Parameters at High Photon Virtualities and Preliminary Cross Sections off
the Neutron,
Presentation and Proceedings,
ECT* Workshop on Nucleon Resonances, Trento, Italy (2015).

"Studies of Excited Nucleons in Exclusive Electroproduction" Write-Up and "Experimental Overview on Baryon Spectroscopy: Current and Future" Presentation leading to the "QCD and Hadron Physics" White Paper, Contributions to the NSAC Long Range Plan, and finally to the 2015 NSAC Long Range Plan itself (2014-15).